1. The problem statement, all variables and given/known data Hi The FSR of a laser with length L is given by Δv = c/2L. If I want to find what Δv is in wavelength, then how do I do this? Obviously I need c=vλ, from which we know that Δv/v = Δλ/λ. But the last equation I can't apply to this case, since it refers to errors around some λ/v. Best, Niles.